Photo-electric tube



Dec. 12, 1933. v, K. zwoRYKlN PHOTO ELECTRIC TUBE Filed June 8, 1927 INVENTOR Wal/mf kaf/67,6.

WITNESSESI ATTORNEY Patented Dec. 12, 1933 PHOTO-ELECTRIC TUBE Vladimir KfZworykin, Swissvale, Pa., assignorV to Westinghouse Electric &V Manufacturing Company, a, corporation of Pennsylvania Application June 8, 1927. Serial'No. 197,245 6 Claims. (Cl. Z50- 275) My invention relates to light-sensitive relays and particularly to such relays employing the photo-electric properties of the alkali metals.

An object of my invention is to produce a lightresponsive relay of the photo-electron type which shall be stable in operation and unvarying inV sensitivity.

A further object of my invention is to produce a photo-electric tube in which the light-sensitive coating may be deposited on a definite and predetermined portion of the tube and which will not vaporize and redeposit upon the parts of the tube intended to remain transparent.

Other objects of my invention will become apparent throughout the following specication taken in connection with the appended drawing, wherein The single figure is a longitudinal section of a photo-electric tube embodying my invention.

A photo-electric tube comprising an evacuated glass container having a pair of electrodes, one of which comprises a surface of alkali-metal, is already known inthe art. In one convenient form of such tube the alkali metal is deposited in 'the form of a thin iilm upon which light is projected through a transparent window in a portion of the tube wall. Y It is a defect of such tubes that the relatively volatile alkali-metal tends to vaporize in the course of time from the surface on which it is originally deposited and to deposit on the portion of the tube Wall which is intended to remain transparent in order to permit the entry of light. This results in a decrease in the sensitivity of the tube both because the photo-sensitive material disappears from the electrode on which it was intended to be the active constituent and because its deposition on a portion suspended in position of the light window cuts o the activating beam.

In accordance with my invention, I avoid both of the above mentioned defects by depositing a thin lm of an alkali-metal to constitute the photo-electric surface, superposed upon a lm of a more stable metal, such as tungsten or molybdenum. This film, being so thin that it is relatively transparent to light, does not, to any substantialrextent, cut down the emission of photo-V electrons by the alkali-metal Ysurface but does have the property of preventing the vaporization of the latter. The'disappearance of the alkali metal from the portion of the tube in which it was originally deposited, and its deposition on other parts of the tube wall, with the consequent defects described above, is thereby avoided.

Referring to the drawing, my photo-electric tube consists of an evacuated glass tube 1, of an ordinary type, through oneend of which are sealed in the wires 2, 3, 4, 5, 6 and 7. Wires 2 and 7 extend above the press and act as supports for an interior glass tube 8.

In the tube, as originally made up, the' glass tube 8 is perfectly clear. Inside each end is insei-ted a copper collar 9 which ts tightly against and is fused to, the glass. rIhe usedjoint and a small length ofthe glass tube adjacent thereto 05 is coated inside with silver by any of the Wellknown silver deposition processes. The copper collars 9 are welded, respectively, to the support wires 2 and 'I and thus hold the glass tube 8 Vfirmlyin position coaxial with the container 1.

The inleading wire 5 is extended high above the press outside 'of the tube 8, and a iilament 10 of tungsten or molybdenumv is positioned in the axis of the tube 8 between the ends of the support wire 5 and the in-leading Wire 4. The 75 inleading wire 6 is extended high above the press and a filament 11 of platinum or nickel coated with potassium nitride or sodium nitride, or some other salt of an alkali-metal, is connected in position inside the tube 8 between the ends of the support wire 6 and the inleading wire 3.

The tube so constructed is evacuated, by methods well-known in the art, to a high-degree of vacuum and, while still on the pump, current is passed through the filament 10, by means of the 35 leads 4 and 5, to heat it to such temperature that the interior of the tube 8 is covered uniformly by a thin lm of metal. The proper thickness may be determined by resistance measurements. For example, a tube one inch long and 1A" 90 inside diameter should have a resistance of one megohm. Current is then passed through the filament 11, by means of its inleading wires, and a thin nlm of the alkali-metal is deposited over the surface of the noble metal. The nlm of the noble metal, made in accordance with the foregoing directions, will be of such thickness as to prevent evaporation of the alkali-metal but still will be transparent to light. In fact, the two lms together may be so thin as to be transparent.

When it is desired to use the photo-electric tube which I have described,A one terminal of a source of electro-motive force may be connected,

through one of the leads 2 and '7, to one of the 105 copper rings 9, and the other terminal of said source may be connected to any one of the re-v maining inleading wires. Current is conducted from the rings 9, through the silver lm, to the potassium and molybdenum films aforesaid and flows from those surfaces to the filament 10 or the filament 11 to which the other terminal of the source has been connected. By varying the amount of light which strikes the surface of the molybdenum and potassium iilm, the amount of current which a given electro-motive force will cause to flow through the interior of tube 8 will vary correspondingly. Current from this source will, therefore, be modulated in accordance with the amount of light permitted to strike the interior surface of the tube 8. Otherwise, the mode of operation of my photo-sensitive tube is similar to that of tubes at present well-known in the art and needs no separate description.

While I have referred to the photo-electric lm deposited on the tube 8 as being of potassium, it will be recognized that a lm of any of the other photo-sensitive metal may be deposited thereon by the same process; rubidium or cs'ium for example. Any of the known processes vfor deriving metallic films, such as distillation from the pure metal instead of a compound like the nitride above described, may be used. n

` Similarly, while the superposed layerrhas been described as being tungsten or molybdenum it will be recognized that any other suitable metal may be deposited by substantially the same process.

While I have described a particular embodiment of my invention as required by the patent statutes, it Will be apparent to those skilled in the art that many modifications of the structure which lI have chosen to describe 'may be made without departure from the principles of my invention. Imdesire,` therefore,..that the terms of the appended claims to be given their broadest reasonable interpretation and that they be limited only by` their express language and by the requirements of the priorrart.

I claim as my invention:

1. A photo-electric cathode comprising a transparent layer of substance having a tendency to vaporize, superimposed upon a transparent layer of a metal having a lower vapor-pressure.

2. An evacuated container enclosing a photoelectric element comprising a transparent film composed of a photo-electric metal and another metal and. means cooperating therewith to make an operating device.

3. An evacuated container enclosing a photoelectric element comprising a transparent film consisting of an alkali metal and a metal having a lower vapor-pressure and means cooperating therewith to make an operating device.

4. A photo-electric tube comprising a vacuum tight container and a transparent layer thereon comprising a photo-electric metal and a metal having lower vapor-pressure and means cooperating therewith to make an operating device.

' 5. A photo-electric tube comprising a container, a cathode structure extending axially through a portion of said container and an anode structure extending axially through said portion of said container, said cathode structure and said anode structure being axially symmetrical, the outer electrode 'structure being transparent.

6. A photo-electric tube comprising a container, a cathode structure extending axially through a portion of said container and an anode structure extending axially vthrough said portion of said container, said cathode structure and said anode structure being axially symmetrical, the outer electrode structure of said cathode and anode structures being spaced from the wall of said portion of the container and also being transparent.

VLADIMIR K. ZWORYKIN. 

